Which magic schools should I choose for the late game? Or should I go for a specific artifact?

In my opinion, mages don't have any problems with knowledge... So, Chaos is not a hero for the late game, when mana is already over 300, because the path to Chaos assumes taking unnecessary abilities (why do mages need machines?, except for the Hafiz, but the path to Chaos implies refusing Ballista), so I would take Chaos and Summoning (Summoning is always relevant, and there is a counterspell against the opponent's Darkness).